1. Field of Art
The field of art to which this invention pertains is graphite fiber reinforced glass material.
2. Description of the Prior Art
While the use of graphite reinforcement in glass composites is not new, because of the potential properties of such a combination there is an ongoing search for the right mix of materials to produce an article which will be satisfactory in properties for a large range of uses. Attempts at accomplishing this goal have included the use of various fibers in place of graphite, such as silicon carbide and aluminum oxide, and attempts at various forms of graphite fiber such as continuous and discontinuous fibers. Because of its ease of fabrication, discontinuous fiber composites have been attempted but have met with little success in the past. For example, an article by Sambell et al entitled "Carbon Fiber Composites with Ceramic and Glass Matrices" (Journal of Materials Science, Vol. 7, pages 663-675, 1972), teaches attempts at fabricating graphite-glass composites from discontinuous fibers. However, when Sambell et al combined their discontinuous fibers with the glass matrix the resulting product did not even have the composite strength of the unreinforced glass matrix. In a follow-up article by the same authors (Journals of Materials Science, Vol. 7, pages 676-681, 1972) the authors went on to use continuous fibers aligned in the matrix to achieve a high composite strength. U.S. Pat. No. 3,681,187 also demonstrates attempts to utilize discontinuous fibers in a glass matrix, and also documents the unsatisfactory results attained by such attempts. Note Table 1 of this reference. And U.S. Pat. No. 3,607,608 further demonstrates the reliance of the prior art on continuous graphite fibers to attain satisfactory strength properties.
Thus, the prior art has turned to continuous graphite fiber reinforced glass to achieve dimensional stability, high strength and stiffness. However, even acceptable graphite glass composites of the past have not provided the workability and strength characteristics desired by the industry. Furthermore, the anisotropic thermal expansion and elastic modulus of such composites have not been acceptable for many industrial uses, for example for various mirror applications. And while attempts such as differing lay-up orientation of the fiber plies has been attempted in the past, the procedure is severely limited by large residual stresses introduced into the composite during cool down from fabrication. Furthermore, there has been some evidence of channeling due to micro-cracking of aligned continuous fiber composites during processing.